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Molecular Spectroscopic Investigations of (E)-1-(4 Methylbenzylidene) Urea Using DFT Method

Hannah Evangalin J1, Bharanidharan S2,* and Dhandapani A3

1Department of Physics, PRIST University, Chennai Campus, Mahabalipuram-603 102, Tamil Nadu, India

2Department of Physics, Bharath Institute of Higher Education and Research, Bharath University, Chennai-600 073, Tamil Nadu, India

3Department of Chemistry, CK College of Engineering and Technology, Cuddalore-607 003, Tamil Nadu, India

*Corresponding Author:
Bharanidharan S
Department of Physics, Bharath Institute of Higher Education and Research,
Bharath University, Chennai-600 073, Tamil Nadu, India.
Tel: +98 11 3368 7901
E-mail: [email protected]

Received date: February 02, 2018; Accepted date: February 28, 2018; Published date: March 08, 2018

Citation: Evangalin JH, Bharanidharan S, Dhandapani A (2018) Molecular Spectroscopic Investigations of (E)-1-(4 Methylbenzylidene) Urea Using DFT Method. Arch Chem Res. Vol.2 No.2:18. doi:10.21767/2572-4657.100018

Copyright: © 2018 Evangalin JH, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

 
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Abstract

The (E)-1-(4-methylbenzylidene)urea (EMBU) molecule have been synthesized and characterized by using FT-IR, FT-Raman and NMR spectral techniques. The quantum chemical calculations of EMBU have been done by using DFT/B3LYP/6- 31G(d,p) basis set. The bond parameters were calculated at same level of theory. The vibrational assignment of EMBU is assigned precisely with the help of potential energy distributions (PED). The hyperconjugative stabilizing interactions are studied by the natural bonding orbital (NBO) analysis. The NLO activity of EMBU is calculated and compared with the standard Urea molecule. The active sites were identified by the molecular electrostatic potential mapped surface. In addition, Mulliken atomic charges and thermodynamic properties were calculated and analyzed.

Keywords

DFT Study; FT-IR; FT-Raman; PED; NMR; NLO

Introduction

Schiff base compounds have been derived from aromatic amines and aromatic aldehydes. Schiff-base compounds exhibit a wide range of biological activities [1], anti-HIV [2], anti-tumor activities [3] and the transition metal complexes [4,5]. Very often it undergoes a variety of chemical reactions, being as a key precursor for new compounds exhibiting diverse molecular structures and properties [6,7]. It is worth mentioning that the salicylaldehyde moiety appears in many compounds exhibiting various biological activity, including reactants used in the design of compounds exhibiting anti-viral activity [8], as well as in reactions resulting in new compounds with anti-cancer [9,10] or anti-microbial activity [11]. It is also present during the synthesis of new products called “aspirin-like molecules” exhibiting antiinflammatory activity [12].

The computational techniques are recently very useful in exploring nonlinear properties theoretically in useful manner. The simultaneous researches in the field of nonlinear materials have influenced the development of efficiencies of organic molecules as NLO material, since organic NLO materials often employ materials and device structures that have direct application to light multiplication.

In our present investigation we have focused on a simple organic molecule (E)-1-(4-methylbenzylidene) urea. We planned to investigate the nonlinear property of that molecule theoretically using first hyperpolarizability calculation. In addition to that, the vibrational spectral studies, NLO activity, NBO analysis, MEP surface and energy gap of the molecule are studied and discussed in detail.

Experimental Details

Synthesis of (E)-1-(4-Methylbenzylidene)urea

Equimolar amount of 4-methylbenzaldehyde and urea were dissolved in 30 ml of absolute ethanol. The mixture was shaken to make homogenous solution. Few drops of catalyst acetic acid were added to increase the rate of reaction. The content was refluxed at 90°C for 3 hours. The completion of the reaction was monitored by thin layer chromatography. After the reaction was completed, the content was cooled the mixture was poured into water. The solid product obtained was filtered and purified using absolute ethanol

image

Spectral measurements

FT-IR, FT-Raman and NMR Spectrum: The FT-IR spectrum of the synthesized EMBU molecule was measured in the Mid- IR (4000–400 cm-1) region at the spectral resolution of 4 cm-1 using on SHIMADZU FT-IR affinity Spectrophotometer (KBr pellet technique) in Faculty of Marine Biology, Annamalai University, Parangipettai. The FT-Raman spectrum was recorded on BRUKER: RFS27 spectrometer operating at laser 100mW in the spectral range of 4000–50 cm-1. FT-Raman spectral measurements were carried out from SAIF, IIT, Chennai. NMR spectral studies were carried out using Bruker 400 MHz spectrometer, using TMS as an internal standard and DMSO-d6 as solvent and recorded at Annamalai University, Annamalainagar, Chidambaram. The 1H and 13C-NMR spectrum were shown in Figure 1.

archives-chemical-cluster-spectra-EMBU

Figure 1: The 1H and 13C-NMR spectra of EMBU.

Computational Details

The quantum chemical calculations were performed at DFT method with B3LYP/6-31G(d,p) basis set using Gaussian 03W [13] program package, invoking gradient geometry optimization [13,14]. The optimized structural parameters were used in the vibrational frequency calculations at the DFT level to characterize all the stationary points as minima. The vibrational modes were assigned on the basis of PED analysis using VEDA4 program package [15]. NBO analysis was done by using NBO 3.1 program.

The Raman activity was calculated by using Gaussian 03W package and the activity was transformed into Raman intensity using Raint program [16] by the expression:

image (1)

Where Ii is the Raman intensity, RAi is the Raman scattering activities, νi is the wavenumber of the normal modes and ν0 denotes the wavenumber of the excitation laser [17].

Results and Discussion

Molecular geometry

The Optimized structure of EMBU molecule is shown in Figure 2 with atom numbering scheme. The bond parameters such as bond lengths, bond angles and dihedral angles values are calculated by DFT/B3LYP/6-31G(d,p) basis set and are listed in Table 1. In this case, the bond length of C-C and C-H are calculated around 1.40 and 1.08 Å, respectively. The bond lengths of related molecule was observed at C-C and C-H values are 1.38, 1.09 Å, respectively [18]. The carbonyl group bond C13=O18 is appeared as π bond character; its bond length value is calculated about 1.2182 Å. Similarly, the π bond character of C=O is observed at 1.212 Å [19], which nearly coincides with calculated value. The σ and π bond characters of N12-C13 and C11=N12 are calculated as 1.4341 and 1.281Å are positively deviated with related molecule data (1.348 Å and 1.273 Å) data [19].

archives-chemical-cluster-optimized-molecular-structure

Figure 2: The optimized molecular structure of (E)-1-(4- methylbenzylidene)urea (EMBU).

Bond Lengths (Å) B3LYP/
6-31G(d,p)
Bond Angles (°) B3LYP/
6-31G(d,p)
Dihedral Angles (°) B3LYP/
6-31G(d,p)
R(1,2) 1.3921 A(2,1,6) 120.8487 D(6,1,2,3) 0.0032
R(1,6) 1.3973 A(2,1,7) 119.6136 D(6,1,2,8) 179.9973
R(1,7) 1.0848 A(6,1,7) 119.5377 D(7,1,2,3) -179.994
R(2,3) 1.4003 A(1,2,3) 120.6796 D(7,1,2,8) -0.0001
R(2,8) 1.0853 A(1,2,8) 119.8559 D(2,1,6,5) -0.0096
R(3,4) 1.4055 A(3,2,8) 119.4645 D(2,1,6,19) 179.957
R(3,11) 1.4605 A(2,3,4) 118.6712 D(7,1,6,5) 179.9879
R(4,5) 1.3847 A(2,3,11) 119.2354 D(7,1,6,19) -0.0456
R(4,9) 1.083 A(4,3,11) 122.0934 D(1,2,3,4) 0.003
R(5,6) 1.4056 A(3,4,5) 120.3294 D(1,2,3,11) 179.9981
R(5,10) 1.0856 A(3,4,9) 118.7107 D(8,2,3,4) -179.991
R(6,19) 1.5076 A(5,4,9) 120.9599 D(8,2,3,11) 0.004
R(11,12) 1.281 A(4,5,6) 121.223 D(2,3,4,5) -0.0026
R(11,15) 1.0958 A(4,5,10) 119.5125 D(2,3,4,9) 179.9914
R(12,13) 1.4341 A(6,5,10) 119.2645 D(11,3,4,5) -179.998
R(13,14) 1.3596 A(1,6,5) 118.2481 D(11,3,4,9) -0.0036
R(13,18) 1.2182 A(1,6,19) 121.3126 D(2,3,11,12) -179.999
R(14,16) 1.0061 A(5,6,19) 120.4392 D(2,3,11,15) 0.0028
R(14,17) 1.0058 A(3,11,12) 123.1686 D(4,3,11,12) -0.0038
R(19,20) 1.0945 A(3,11,15) 116.9094 D(4,3,11,15) 179.9978
R(19,21) 1.0914 A(12,11,15) 119.922 D(3,4,5,6) -0.004
R(19,22) 1.0944 A(11,12,13) 115.0758 D(3,4,5,10) 179.9926
    A(12,13,14) 110.1617 D(9,4,5,6) -179.998
    A(12,13,18) 126.0669 D(9,4,5,10) -0.0012
    A(14,13,18) 123.7714 D(4,5,6,1) 0.01
    A(13,14,16) 119.3699 D(4,5,6,19) -179.957
    A(13,14,17) 119.9243 D(10,5,6,1) -179.987
    A(16,14,17) 120.7058 D(10,5,6,19) 0.0466
    A(6,19,20) 111.0369 D(1,6,19,20) -119.878
    A(6,19,21) 111.4884 D(1,6,19,21) 0.5522
    A(6,19,22) 111.0578 D(1,6,19,22) 121.0241
    A(20,19,21) 107.9612 D(5,6,19,20) 60.0881
    A(20,19,22) 107.1337 D(5,6,19,21) -179.482
    A(21,19,22) 107.983 D(5,6,19,22) -59.0101
        D(3,11,12,13) -179.998
        D(15,11,12,13) 0.0003
        D(11,12,13,14) -179.996
        D(11,12,13,18) 0.0049
        D(12,13,14,16) 179.9973
        D(18,13,14,17) -179.998

Table 1: The optimized bond parameters of EMBU.

The bond angles of N12-C13-O18 and N14-C13=O18 is calculated about 126.06 and 123.77°, respectively. Similarly, the reported molecule calculated the bond angle value of N-C=O is 123.36°, which nearly matches with calculated values [18]. These results fairly explore that, during the course of rotation of the bond to the entire molecule gets disturbed and the properties of the molecule also changes. From the literature [20] and our theoretical investigation, the optimized structure is more stable.

Vibrational assignments

The EMBU molecule belongs to C1 point group symmetry. It consists of 22 atoms and 60 normal modes of vibrations are distributed among the symmetry species as;

Γ3N-6 = 41′ (in-plane) + 19′′ (Out-of-plane)

All these modes are found to be are active both in the IR and Raman absorption. The harmonic wavenumbers are calculated using B3LYP/6-31G(d,p) basis set and compared with recorded vibrational frequencies of FT-IR and FT-Raman spectra, respectively. Some discrepancies could be identified in between harmonic and observed frequencies, which are scaled down by proper scale factor [21,22]. The vibrational assignments are given in Table 2. The combined recorded and theoretical spectra are shown in Figures 3 and 4.

Mode No Theoretical Experimental IR Intb Raman Intc Vibrational Assignments PED≥(10%)d
Un Scaled Scaleda IR Raman
1 3745 3603 3606   16.8 0.9  νN14H16(100)+νN14H17(100)
2 3608 3471 3460   20.4 2.5  νN14H16(100)+νN14H17(100)
3 3199 3077     0.7 1.4  νC4H9(95)
4 3177 3056 3061   3.8 3.2  νC1H7(97)+νC2H8(95)
5 3160 3040     1.6 1.8  νC1H7(97)+νC2H8(95)
6 3160 3040     4.3 1.5  νC5H10(89)
7 3107 2989 2987   4.6 1.6  νC19H21(99)
8 3074 2957     3.5 2.7  νC19H20(90)+νC19H22(90)
9 3052 2936 2929   2.8 1.1  νC11H15(100)
10 3025 2910     6.8 9.8  νC19H20(90)+νC19H21(99)+νC19H22(90)
11 1762 1695 1672 1648 111.6 1.5  νO18C13(88)
12 1671 1607     52.2 33.9  νN12C11(66)
13 1646 1583 1598   45.4 100  νC4C5(53)+νC2C1(62)+νC2C3(48)
14 1602 1541   1539 0.4 0.9  νC4C3(47)+νC6C5(79)+βH16N14H17(83)+βC2C1C6(57)
15 1595 1534 1506   117.4 27.1  βH16N14H17(83)
16 1543 1484   1468 0.9 3.5  βH7C1C2(54)+βH9C4C5(66)+βH10C5C4(75)+βC4C3C2(65)
17 1494 1438 1435   4.5 4.9  βH21C19C6(76)+βH20C19H22(84)
18 1486 1429     2.1 1.4  βH20C19C6(85)+ГC19H20C6H21(91)
19 1440 1385     4.5 2.9  νC4C5(53)+νC2C1(62)
20 1415 1361 1354   0.4 4.4  βH20C19H22(84)+ГC19H21H22H20(80)
21 1400 1347     18.4 2.8  νN12C11(66)+βH15C11N12(82)
22 1341 1290 1298   28.1 2.4  νN14C13(55)+βH9C4C5(66)+βH10C5C4(75)
23 1338 1287     0.7227 1.3  νC2C3(48)+νC6C5(79)
24 1325 1275     100 15  νN14C13(55)+βH16N14C13(56)+βH15C11N12(82)
25 1246 1199     31.2 30  νC11C3(50)+βH7C1C2(54)+βH10C5C4(75)+βH15C11N12(82)
26 1229 1182   1174 3.9 9.6  νC2C1(62)+βC1C6C5(51)+νC19C6(64)
27 1198 1152     19.8 22.5  βH7C1C2(54)+βH8C2C1(50)+βH9C4C5(66)+βH10C5C4(75)
28 1138 1095     1.7 1.1 νC4C5(53)+νC2C1(62)+βH7C1C2(54)+βH8C2C1(50)+βH9C4C5(66)
29 1098 1056     1.1 8.5  νO18C13(88)+νN14C13(55)+βH16N14C13(56)
30 1061 1021     1.5 0  βH20C19C6(85)+ГC19H20C6H21(91)
31 1053 1013 1002 1009 0.9 0.9  τH15C11N12C13(82)
32 1035 996     2.3 0.3  βC1C6C5(51)+βC2C1C6(57)+βC6C5C4(57)
33 1008 969     4.1 0.6  νC6C5(79)+βH21C19C6(76)
34 999 962 950   0 0  ГC4C3C5H9(81)+τH10C5C4C3(85)
35 971 934     0.1 0  τH7C1C2H8(77)
36 935 899     31 4.6  νN12C13(51)+βN12C11C3(75)
37 874 840 867   0 6.8  νC2C3(48)+νC4C3(47)+νC11C3(50)
38 856 824 829   0.9 0  τH7C1C2C3(82)+ГC4C3C5H9(81)+τH10C5C4C3(85)
39 838 806     11 0  τH7C1C2C3(82)+τH10C5C4C3(85)
40 786 756     0.2 6.6  νC19C6(64)+βC4C3C2(65)
41 780 750 746   0.1 0  τC3C11N12C13(68)+ГO18N12N14C13(70)
42 723 695     1.3 0.2  τC1C6C2C3(82)+τC3C2C4C5(83)+τC1C6C4C5(77)
43 657 632     1.9 1.6  νC6C5(79)+βN12C13O18(65)+βC6C5C4(57)
44 647 623 613   3.6 2.9  βC1C6C5(51)+βN12C13O18(65)
45 608 585   546 0.2 0  ГH16N14C13N12(93)
46 563 542     1 0.8  βN12C11C3(75)+βN14C13N12(80)+βC2C3C11(68)
47 512 492     8.7 0.1  τC3C2C4C5(83)+τC1C6C4C5(77)
48 509 489 476   3.4 0.2  βC1C6C5(51)+βN14C13N12(80)
49 422 406     0.1 0.1  τC1C6C2C3(82)+τC1C6C4C5(77)
50 371 357     1.6 0.8  βN14C13N12(80)+βC2C3C11(68)+βC5C6C19(75)
51 352 339     0.9 1.4  τC3C2C4C5(83)+τC4C5C6C19(68)+τC1C2C3C11(79)
52 298 287     0.5 1.8  βN14C13N12(80)+βC2C3C11(68)+βC5C6C19(75)
53 240 231     1.2 3.2  νC11C3(50)+βN12C13O18(65)+βC4C3C2(65)+βC13N12C11(61)
54 230 221     61 0.5  ГN14H16C13H17(89)
55 189 182     0 0.8  τC4C3C11N12(77)+τC3C2C4C5(83)+τC4C5C6C19(68)
56 151 146   132 0.9 0.3  τC4C3C11N12(77)+τN14C13N12C11(95)+τC3C11N12C13(68)
57 94 91   101 0.3 2.6  βN12C11C3(75)+βC2C3C11(68)+βC13N12C11(61)
58 63 60   63 0 2.2  τC3C11N12C13(68)+τC1C2C3C11(79)
59 32 31     2.3 1.5  τC4C3C11N12(77)+τN14C13N12C11(95)
60 15 15     0 22.8  τH22C19C6C5(91)

Table 2: The fundamental vibrational assignments of EMBU.

archives-chemical-cluster-combined-Theoretical

Figure 3: The combined Theoretical and Experimental IR spectra of EMBU.

archives-chemical-cluster-FTRaman

Figure 4: The combined Theoretical and Experimental FTRaman spectra of EMBU.

C=O Vibrations: The C=O stretching vibrations has been most extensively studied by IR and Raman spectroscopy. This multiply bonded group is highly polar and therefore gives rise to an intense IR absorption band, because of the different electro negativities are distributed between the two atoms [23]. The lone pair oxygen atom also determines the nature of the carbonyl group. In this study, the weak bands observed at 1672 and 1648 cm-1 in FTIR and FT-Raman spectra are assigned to C=O stretching vibration and its corresponding harmonic value lies at 1692 cm-1 (mode no: 11). This vibrational assignment is further supported by PED 88%.

C-C Vibrations: Generally, the phenyl ring carbon-carbon (C-C) stretching vibrations are observed in the region of 1625-1590, 1590-1575, 1540-1470, 1465-1430 and 1380-1280 cm-1 by Varsanyi (1974) [24]. In the present study, the FT-Raman bands observed at 1539 and FTIR band observed at 1598 cm-1 and are assigned to C-C stretching vibrations and their corresponding harmonic values appeared in the range of 1583 and 1541 cm-1 (mode nos: 13 and 14). These assignments are good agreement with literature [25].

The C-C in-plane bending vibrations observed at 1174 cm-1 in Raman and 613 cm-1 in IR spectrum and its corresponding calculated value appeared at 1182 and 623 cm-1 (mode no: 26 and 44). The ГC4C3C5H9 mode predicted at 962 cm-1 (mode no: 34) is in agreement with IR band observed at 950 cm-1 with the help of PED 81%.

C-H Vibrations: In General, the CH stretching modes are expected to occur in the range 2900-3200 cm−1 [26,27]. In our study, C-H vibrations are observed at 3061, 2987 and 2929 cm-1 in FTIR spectrum. The corresponding harmonic frequencies lies at 3056, 2989 and 2936 cm-1 (mode nos: 4, 7 and 9) are belong to the same mode. These results were good agreement with experimental value with PED >95%. In benzene like molecule the C-H inplane bending vibrations are appeared in the region 1000-1300 cm−1 and are usually weak intense. In our study, the frequency of the βCH vibrations are calculated in the region of 1438-1290 cm-1 (mode nos: 16 and 22) for this molecule. These modes are observed in the FTIR: 1298 cm-1/FT-Raman: 1468 cm-1 spectra with weak intensity. The harmonic frequencies in the range 962 cm-1 (mode nos: 34) and FTIR band observed at 950 cm-1 assigned to ΓCH mode. These assignments are find support from PED.

N-H Vibrations: In general, the N-H stretching vibrations observed in the region 3400-3200 cm-1 [28]. In the present case, the N-H band assigned at 3460 cm-1 (mode no: 2). This assignment is further justified on the basis of their calculated PED value (100 %). The calculated wavenumber for βN-H (1534 cm-1/ mode no: 15) and ΓN-H (585 cm-1/ mode no: 45) modes well reproduced the experimental ones in FT-IR (1506 cm-1) and FT-Raman (546 cm-1) spectra with PED values (83% and 93%), respectively.

C-N Vibrations: The assignment of C=N stretching frequency is a rather difficult task since there are problems in identifying these frequencies from other vibrations. The ring C–N vibrations are appeared in the region 1650–1550 cm−1 [29]. The bands obtained at 1598 cm-1 in FT-IR and at 1539 cm-1 in FT-Raman spectra have been assigned to C=N stretching vibrations of title molecule. The corresponding theoretical wavenumber lies at 1583 and 1541 cm-1, which is comparable to experimental wavenumber with PED contribution ≥ 45%. Silverstein et al., [30] assigned C–N stretching vibrations occurred in the region 1382–1266 cm-1 for the aromatic amines. The C-N stretching vibrations of title molecule were obtained at 1298 cm-1 in FT-IR spectrum. The band calculated at 1290 cm-1 from DFT is assigned to C-N stretching vibration of the present molecule.

NLO property

In this study, the electronic dipole moment, molecular polarizability, anisotropy of polarizability and molecular first hyperpolarizability of EMBU were calculated at DFT/B3LYP/6- 31G(d,p) basis set and are presented in Table 3. It is well-known that the higher values of dipole moment, molecular polarizability, and hyperpolarizability which enhances the NLO property. Urea is one of the prototypical molecule used in the study of the NLO property of molecular systems, and thus, it was used frequently as a threshold value for comparative purposes. The first hyperpolarizability value of EMBU was calculated as 10.595 × 10−30 esu. According to these result, the β0 value of present molecule is twenty-eight times larger than the magnitude of urea, which implies that the title molecule might become a kind of good NLO material.

Parameters B3LYP/6-31G(d,p)
             Dipole moment ( μ )                               Debye
μx -1.1362
μy -0.8895
μz 0.0003
μ 1.4429 Debye
Polarizability ( α0  )x10-30esu
αxx 214.95
αxy -4.99
αyy 125.77
αxz -0.02
αyz 0.00
αzz 70.94
α0 3.1476x10-30esu
Hyperpolarizability ( β0)x10-30esu
βxxx 1383.41
βxxy 211.90
βxyy -151.05
βyyy 30.28
βxxz 0.10
βxyz 0.09
βyyz -0.25
βxzz -24.15
βyzz -31.28
βzzz 0.19
β0 10.595x10-30esu

Table 3: The NLO measurements of EMBU.

NBO analysis

The NBO analysis provides an efficient method for studying intraand inter-molecular bonding and interaction among bonds, and also provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems [31].

In this present study, the NBO analysis has been carried out with DFT/B3LYP/6-31G(d,p) level of basis set and which deals the intra-molecular charge transfer within the molecule. In any molecule, the π character of the bond plays an important role when compare with σ bond character. In such a way that this molecule delivers maximum delocalization energy during the transition between π and π* bond whereas the ED of the donor (Lewis) bond decreases with increasing of ED of acceptor (Non- Lewis) bonds. In our case, the conjugative π bonds in the phenyl ring shows maximum delocalization during the interaction with π* acceptor bonds. It is evident from our title compound that the energy transfer from πC1-C6 to π*C2-C3, πC4-C5 to π*C1-C6 and πC2-C3 to π*C11-N12 are reveals the hyperconjucative energy about 97.74, 92.51 and 86.69 KJ/mol, respectively. Similarly, the lone pair atoms such as oxygen and nitrogen also transfer more energy to donor and acceptor bonds. The LP(1)N14 to C13-O18 and LP(2)O18 to N12-C13 bonds transfer the energy about 252.71 and 106.78 KJ/mol, respectively and are listed in Table 4. The maximum hyperconjugative E(2) energy of lone pair atoms during the intra-molecular interaction, which leads the molecule towards medicinal and biological applications.

Type Donor NBO (i) ED/e Acceptor NBO (j) ED/e E(2)
KJ/mol
E(j)-E(i)
a.u.
F(i,j)
a.u.
π -π* BD (2) C1 - C6 1.63787 BD*(2) C2 - C3 0.37327 97.74 0.28 0.072
BD*(2) C4 - C5 0.26902 69.12 0.29 0.063
BD*(1) C19 - H20 0.0084 10.96 0.65 0.041
BD*(1) C19 - H22 0.0083 10.75 0.65 0.04
π -π* BD (2) C2 - C3 1.62997 BD*(2) C1 - C6 0.32641 73.43 0.29 0.064
BD*(2) C4 - C5 0.26902 81.46 0.29 0.068
BD*(2) C11 - N12 0.13157 86.69 0.28 0.072
π -π* BD (2) C4 - C5 1.67949 BD*(2) C1 - C6 0.32641 92.51 0.29 0.071
BD*(2) C2 - C3 0.37327 75.06 0.28 0.065
π -π* BD (2) C11 - N12 1.88985 BD*(2) C2 - C3 0.37327 32.64 0.35 0.05
BD*(2) C13 - O18 0.32592 86.02 0.35 0.08
π -π* BD (2) C13 - O18 1.99066 BD*(2) C11 - N12 0.13157 8.54 0.38 0.026
BD*(2) C13 - O18 0.32592 6.86 0.38 0.024
n -σ* LP (1) N12 1.9205 BD*(1) C3 - C11 0.03167 7.7 0.85 0.036
BD*(1) C11 - H15 0.04014 44.06 0.77 0.081
BD*(1) C13 - N14 0.06619 8.41 0.84 0.037
BD*(1) C13 - O18 0.02348 38.07 0.99 0.086
n -π* LP (1) N14 1.74159 BD*(2) C13 - O18 0.32592 252.71 0.28 0.119
n -σ* LP (1) O18 1.97754 BD*(1) N12 - C13 0.08854 9.79 1.07 0.045
BD*(1) C13 - N14 0.06619 8.54 1.15 0.044
n -σ* LP (2) O18 1.8497 BD*(1) N12 - C13 0.08854 106.78 0.63 0.115
BD*(1) C13 - N14 0.06619 97.61 0.71 0.117

Table 4: The NBO analysis of EMBU.

HOMO-LUMO analysis

The HOMO and the LUMO are called frontier molecular orbitals as they lie at the outermost boundaries of the electrons of the molecules. The HOMO and LUMO are the main orbitals responsible for chemical stability. The HOMO–LUMO orbitals of the EMBU are as shown in Figure 5. The calculated values of the HOMO and LUMO energies and band gap energy are listed in Table 5. The positive and negative phases are represented in green and red color, respectively. HOMO represents the electrondonating ability of a molecule, whereas LUMO indicates its ability to accept electrons. The frontier orbital gap helps to characterize the chemical reactivity and kinetic stability of the molecule. In the present study, the energy gap have been calculated using B3LYP/6-31G(d,p) level are 4.76415 eV. This small energy gap is associated with high chemical reactivity and low kinetic stability.

archives-chemical-cluster-frontier-molecular

Figure 5: The frontier molecular orbitals of EMBU.

Orbitals Energy (a.u) Energy (eV)
39O -0.30489 -8.29636
40O -0.279438 -7.60379
41O -0.272717 -7.4209
42O -0.258641 -7.03788
43O -0.255165 -6.94329
44V -0.080083 -2.17914
45V -0.029496 -0.80262
46V -0.012194 -0.33181
47V -0.006217 -0.16917
48V 0.00296 0.080545

Table 5: The frontier molecular orbitals of EMBU.

MEP analysis

The MEP surface map was calculated at B3LYP/6-31G(d,p) method. MEP is related to the ED. It is very useful descriptor in understanding the sites for electrophilic attacks and nuleophilic reactions as well as hydrogen bonding interactions [32]. The importance of MEP lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of colour grading as shown in Figure 6. Potential increases in the order red < orange < yellow < green < blue. The colour code of these maps, where blue indicates the strongest interaction and red indicates the strongest repulsion. In this study, the negative region is located over the carbonyl group and the positive region is located over Hydrogen atom in the imine linkage.

archives-chemical-cluster-MEP-surface-EMBU

Figure 6: The MEP surface of EMBU.

Mulliken charges

Mulliken populations can be used to characterize the electronic charge distribution in a molecule and the bonding, anti-bonding, or non-bonding nature of the MOs for pair of atoms [33]. Mulliken atomic charge calculation has an important role in the application of quantum chemical calculation to molecular system. The total atomic charges of EMBU are calculated by Mulliken population analysis with DFT method B3LYP/6-31G(d,p) basis set are listed in Table 6. The Mulliken atomic charge plot for EMBU is plotted in Figure 7. The most positive charges calculated at C3/0.636162 and C6/0.651105 in the present molecule. The C6 atom has high positive charge due to the attachment of methyl group. Similarly, the negative charges were calculated at C1/-0.764424 and C19/-0.612242, respectively. From the results, C1 atom shows the higher negative charge due to the presence aromatic ring. The nitrogen and oxygen atoms also be a negative charge such as N12/-0.118445, N14/- 0.393447 and O18/-0.362573, respectively.

Atoms Charges Atoms Charges
1C -0.764424 12N -0.118445
2C -0.567188 13C 0.247575
3C 0.636162 14N -0.393447
4C -0.272493 15H 0.187019
5C -0.251654 16H 0.30635
6C 0.651105 17H 0.266017
7H 0.138265 18O -0.362573
8H 0.161024 19C -0.612242
9H 0.179329 20H 0.159652
10H 0.176258 21H 0.152303
11C -0.077157 22H 0.158565

Table 6: The Mulliken atomic charges of EMBU.

archives-chemical-cluster-atomic-charges-plot

Figure 7: The Mulliken atomic charges plot of EMBU.

Thermodynamic properties

The standard thermodynamic functions: heat capacity (C0 p,m), entropy (S0 m) and enthalpy changes (H0 m) for the EMBU were calculated using DFT method at B3LYP/6-31G(d,p) basis set and are listed in Table 7. Therefore, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 1000 K due to the molecular vibrational intensities increase with temperature [34]. The correlation equations among thermodynamic functions due to the temperature were fitted by quadratic, linear and quadratic formula and the corresponding fitting factors (R2) for these thermodynamic properties are 0.99957, 0.99997 and 0.99971. The corresponding fitting equations are as follows, and the correlation graphs are shown in Figure 8.

T S (J/mol.K) Cp (J/mol.K) ΔH (KJ/mol)
100 322.65 102.31 7.77
200 431.05 157.53 21.14
300 504.31 248.38 39.40
400 572.12 314.48 68.66
500 656.22 361.16 102.77
600 746.02 414.85 129.31
700 811.21 450.54 171.54
800 852.00 459.45 237.19
900 928.71 498.26 285.37
1000 981.74 523.05 335.81

Table 7: Thermodynamic properties of EMBU at different temperatures.

archives-chemical-cluster-thermodynamic-properties

Figure 8: The thermodynamic properties of EMBU at different temperatures.

C0p,m = -1.73055 + 0.1542T – 6.3237x10-5 T2 (R2 = 0.99957)

S0m = 3.06457 + 0.13745T – 1.83581x10-5 T2 (R2 = 0.99997)

ΔH0m = 107.82213 + 0.00557T + 1.88572x10-5 T2 (R2 = 0.99971)

All the thermodynamic data are supportive information for further study on the molecule.

Conclusion

The quantum chemical calculations were performed at DFT method for the first time to the EMBU molecule. The bond parameters (bond lengths, bond angles and dihedral angles) are agree well with the related molecule XRD data. The observed and calculated wavenumbers of EMBU are well supported by the literature values. The hyperpolarizability (β0) value of EMBU molecule is calculated about 10.595x10-30 esu, which is twentyeight times greater than that of standard urea. The NBO analysis reveals that, the charge transfer occur within the molecule and the maximum energy takes place during π-π* transition. The energy gap of EMBU molecule is calculated at 4.76415 eV, which leads the title molecule to become less stable and more reactive. The reactive sites of EMBU molecule is predicted by MEP surface. In addition, Mulliken atomic charges and thermodynamic properties are also calculated and analyzed.

References

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